There has been much discussion over the last 4 months about a growing and serious nature of QR code cyber attacks against mobile users. The reported risk is that QR codes may become popular targets for mobile attacks because once a user scans the QR code with a mobile device's camera there is no indication or guarantee for where they will be taken and whether the destination site or app is safe.
Both iOS and Android devices are at risk, unfortunately. On iOS devices, users can be taken to a site that will install malware, like keyloggers. And with an Android system, a malicious application can be installed on the device and run in the background without a user ever knowing it was there.